The heart is a four-chambered pump that moves blood efficiently through the vascular system. Blood enters the heart through the vena cava and flows into the right atrium. From the right atrium, blood flows through the tricuspid valve and into the right ventricle, which then contracts and forces blood through the pulmonic valve and into the lungs. Oxygenated blood returns from the lungs and enters the heart through the left atrium and passes through the mitral valve into the left ventricle. The left ventricle contracts and pumps blood through the aortic valve into the aorta and to the vascular system.
The mitral valve consists of two leaflets (anterior and posterior) attached to a fibrous ring or annulus. In a healthy heart, the mitral valve leaflets close during contraction of the left ventricle and prevent blood from flowing back into the left atrium. Due to various cardiac diseases, however, the mitral valve annulus may become distended causing the leaflets to remain partially open during ventricular contraction and thus allow regurgitation of blood into the left atrium. This results in reduced ejection volume from the left ventricle, causing the left ventricle to compensate with a larger stroke volume. However, the increased workload eventually results in dilation and hypertrophy of the left ventricle, further enlarging and distorting the shape of the mitral valve. If left untreated, the condition may result in cardiac insufficiency, ventricular failure, and ultimately death.
It is common medical practice to treat mitral valve regurgitation by either valve replacement or repair. Valve replacement involves an open-heart surgical procedure in which the patient's mitral valve is removed and replaced with an artificial valve. This is a complex, invasive surgical procedure with the potential for many complications and a long recovery period.
Mitral valve repair includes a variety of procedures to repair or reshape the leaflets to improve closure of the valve during ventricular contraction. If the mitral valve annulus has become distended, a frequent repair procedure involves implanting an annuloplasty ring on the mitral valve annulus. The annuloplasty ring generally has a smaller diameter than the annulus, and when sutured to the annulus the annuloplasty ring draws the annulus into a smaller configuration, bringing the mitral valve leaflets closer together, and allowing improved closure during ventricular contraction. Annuloplasty rings may be rigid, flexible or a combination, having both rigid and flexible segments. Rigid annuloplasty rings have the disadvantage of causing the mitral valve annulus to be rigid and unable to flex in response to the contractions of the ventricle, thus inhibiting the normal, three dimensional movement of the mitral valve that is required for it to function optimally. Flexible annuloplasty rings are frequently made of Dacron® fabric and must be sewn to the annular ring with a line of sutures. This eventually leads to scar tissue formation and loss of flexibility and function of the mitral valve. Similarly, combination rings must generally be sutured in place and also cause scar tissue formation and loss of mitral valve flexibility and function.
Another approach to treating mitral valve regurgitation requires a flexible elongated device that is inserted into the coronary sinus and adapts to the shape of the coronary sinus. The device then undergoes a change that causes it to assume a reduced radius of curvature and, as a result, causes the radius of curvature of the coronary sinus and the circumference of the mitral annulus to be reduced. While likely to be effective for modest changes in the size or shape of the mitral annulus, this device may cause significant tissue compression in patients requiring a larger change in the configuration of the mitral annulus. Alternatively, the coronary sinus in a particular individual may not wrap around the heart far enough to allow effective encircling of the mitral valve, making this treatment ineffective. Furthermore, leaving a device in the coronary sinus may result in formation and breaking off of thrombus that may pass into the right atrium, right ventricle, and ultimately the lungs causing a pulmonary embolism. Another disadvantage is that the coronary sinus is typically used for placement of a pacing lead, which may be precluded with the placement of the prosthesis in the coronary sinus.
It would be desirable, therefore to provide a method and device for reducing mitral valve regurgitation that would use minimally invasive surgical techniques, but would overcome the limitations and disadvantages inherent in the devices described above.